Field
This disclosure relates generally to an apparatus and method for inserting valves into a pipeline, and more specifically to an insert valve that may be placed in an in-service pipeline without interruption of service through shutdown or line stops.
Description of the Related Art
Pipelines are used to transport a wide variety of fluids, including water, natural gas, oil, and chemicals. The method of installation for new pipelines (and related components) is completely different than service and repair of existing pipelines. At various times, existing pipes and pipelines need to be inspected, serviced, repaired, and/or maintained. The task of inserting a valve in a line containing fluid under pressure (e.g., a municipal water line or natural gas line) without otherwise shutting down the line during the installation can be expensive, inconvenient, and time consuming. Yet the need to do so is commonplace. In many instances, it is desired to insert a valve into an in-service pipeline. In these situations, “line stops” typically are used to temporarily stop flow of in-service piping systems by insertion of a plugging device and installation of a looped bypass. In general, “hot tapping” is the method of making a connection to existing piping or pressure vessels without the interruption or emptying of that section of pipe, which allows a pipe to be in operation while maintenance or modifications are being done to it. Hot tapping is generally the first step in line stopping. Various types of hot taps, line stops, and other stops are commercially available. FIG. 1 shows standard hot tap machine 120 (installed with a cutter/pilot assembly, hot tap housing bleeder valve, and measuring rod) coupled to temporary valve 113 that is coupled to piping system 101 via hot tap fitting 111.
The Applicant offers a wide variety of hot tap and line stop solutions for making branch connections into operating piping systems, heat exchangers, vessels, columns, and tanks. In general, for a line stop, a fitting is installed around a pipe and a hole is tapped into the pipeline within the fitting. A line stop head or other similar device is inserted into the hole to stop flow, allowing for maintenance or a valve installation. A completion plug or other similar device is locked into place to allow the temporary valve to be removed, and a blind flange is installed to complete the work. Variously specialty line stops are available, such as for insertions into the radius of a pipe, as well as other stops depending on particular needs, such as freeze stops and bag stops. In a typical hot tap setup, a flanged nozzle or fitting is welded or attached to a pipeline and a tapping valve is attached to this flange or fitting. After the necessary valves or fittings are installed, a hole saw or other cutter makes an opening into the pipeline.
For existing pipelines, conventional installations of a valve and/or repair of a section of pipe require typically multiple isolations, hot taps, and fittings. For example, as illustrated in FIG. 2A, a “double line stop” is a procedure in which two fittings 221, 223 are welded to a section of pipe 201 and temporary valve 211, 213 is installed onto each fitting (such as via a hot tap procedure, described above), after which the two line stops are set and pressure vented. Any work between the two line stops is completed, the line stops are equalized and removed, and completion plugs are set and the temporary valves are removed. A “double block and bleed” is a procedure in which two line stops are set and the pressure vented between and downstream of both line stops. The primary line stop holds the pressure while the secondary line stop ensures a safe seal. Once the work downstream is completed, the line stops are equalized and removed, and completion plugs are set and the temporary valves are removed. For in-service lines, as illustrated in FIG. 2B, a “double line stop” with bypass loop 240 is typically used. Four fittings 221, 231, 223, 233 are welded or bolted to pipeline 201. Temporary valves are installed on each fitting and bypass hot taps and line stop taps are completed. The temporary bypass is installed and the temporary bypass valve is opened. The piping section 205 between the two line stops is de-pressurized and repaired. Once the work is completed, the repaired section is equalized, the line stops are removed, the temporary bypass is removed, and completion plugs are set in the four fittings.
For in-service pipeline repair (pipelines which contain fluid under pressure), it may be necessary to install multiple valves to achieve double block functionality and insertion of a valve. Numerous techniques and equipment exist for such repair. One existing way of inserting a valve into a pipeline without shutting down service starts by cutting a hole in the pipe with a conventional hot-tapping hole saw apparatus. A valving apparatus is then added that forces a rubber plunger into the hole. The rubber plunger expands enough to block the line. Withdrawing the plunger unblocks the line. One problem with the rubber plunger technique is that success of the valving apparatus depends on the internal size and condition of the pipe. In addition, an old, corroded or otherwise damaged and weakened pipe is subject to being broken. Furthermore, pushing a plug through a tapped hole subjects the rubber gate to being cut by the sharp edges of the hole cut in the pipe each time the gate is opened and closed. TDW Services offers a SHORTSTOPP® and STOPPLE® plugging system designed to serve as temporary block valve without interrupting service. For example, in a STOPPLE® train plugging system, a double-block-and-bleed design is used to insert two plugging heads through a single pipeline fitting. Two plugging heads are linked into a “train” to provide the added assurance of two seals at each isolation point. However, the STOPPLE® train plugging system still requires the use of two isolation points. Another known valve is described in U.S. Pat. No. 6,776,184, which describes an insertion valve and installation method that, among other things, provides a gate valve stopping mechanism that is configured to seal without contact to the pipe. Likewise, other known valves do not allow for the removal of the valve's internal components once installed in a pipeline without shutting down the operation.
There is a need for a system that allows the insertion of a valve in an in-service pipeline by installing only a single valve and/or hot tapping at a single location. There is a need for a system that allows for the repair, servicing, replacement, and/or removal of a valve without the use of additional line stops. A need exists for a single valve and insert assembly for in-service pipelines without having to use line stops or additional downstream isolations. A need exists for a single valve assembly that allows a verifiable double block and bleed in an in-service line. A need exists for a valve assembly that does not depend on pipeline wall thickness or condition. A need exists for a valve assembly that allows for full-bore opening for pigging operations and in-line inspection. A need exists for a valve and insert assembly that is less expensive and easier to install than current approaches and still utilizes conventional hot tap and installation equipment. A need exists for a valve to be installed and not expose workers unsafely to open end pipe.